1. Field of the Invention
The present invention relates to a semiconductor photosensitive device and a semiconductor device which are optimum for application into an optical pickup, for example, of optical disc apparatus and a method for forming such devices.
2. Description of Related Art
A photo sensor is generally used for an optical pickup of an optical disc apparatus such as a compact disc apparatus and minidisc apparatus. Moreover, as the recent technology, a photosensitive element such as photodiode and a semiconductor element tend to be integrated into one chip. In the case of using a discrete photosensitive element, wirings are required for connecting the photosensitive element to a photodetecting circuit. However, such wirings are easily influenced by external disturbances from power supplies and electrical appliances such as television receivers, etc. Since a small current flows through the photosensitive element, a signal from the photosensitive element receives a large influence from external disturbances. Integration of the photosensitive element and semiconductor element into one chip enables reduction in size of an optical pickup and increases allowance for external noise disturbances.
A semiconductor photosensitive element to be used for an optical pickup of a compact disc apparatus (hereinafter, it is sometimes called a semiconductor photosensitive element for compact disc apparatus) is generally composed of six photosensitive regions A, B, C, D, E, and F as illustrated in the schematic layout of FIG. 1A. Four photosensitive regions A, B, C, and D are provided for detecting a focus error signal and a digital signal. Meanwhile, the photosensitive regions E and F are provided for detecting a tracking error signal. The characteristics required for the photosensitive regions A, B, C, and D and that required for the photosensitive regions E and F are different. That is, the excellent frequency characteristic is required for the photosensitive regions A, B, C, and D in order to detect digital signal. Meanwhile, such frequency characteristic is not so much important for the photosensitive regions E and F because these photosensitive regions detect the tracking error signal of comparatively low frequency. Instead, the excellent photoelectric conversion characteristic is required for the photosensitive regions E and F because these regions are irradiated with the light having comparatively low intensity.
A semiconductor photosensitive element used for optical pickup of a minidisc apparatus (hereinafter semiconductor photosensitive element for minidisc apparatus) is generally composed of eight photosensitive regions A, B, C, D, E, F, G, and H as illustrated in the schematic layout of FIG. 1B. Unlike the semiconductor photosensitive element used with compact disc arrangements, four photosensitive regions A, B, C, and D are provided in the semiconductor photosensitive element for minidisc apparatus for detecting a focus error signal. The photosensitive regions E and F are provided for detecting a tracking error signal. Moreover, the photosensitive regions G and H are provided for detecting a digital signal. Excellent photoelectric conversion characteristic is required for the photosensitive regions E and F because these regions are irradiated with the light beam having comparatively lower intensity. Meanwhile, excellent frequency characteristic is required for the photosensitive regions G and H to detect a digital signal. However, higher photoelectric conversion characteristic and frequency characteristic are not required for the photosensitive regions A, B, C, and D because these regions are radiated with the light beam having higher intensity and the focus error signal has comparatively lower frequency.
As explained above, different characteristics are required for respective photosensitive regions of the semiconductor photosensitive element used for optical pickup of optical disc apparatus. However, since the photoelectric conversion characteristic and frequency characteristic are in the trade-off relationship, when the photoelectric conversion characteristic, for example, is raised, the frequency characteristic is lowered. Therefore, a semiconductor photosensitive element, mainly having improved the photoelectric conversion characteristic, is used for optical pickup.
Furthermore, when a photosensitive element and a semiconductor element are integrated into one chip, a problem arises that such photosensitive element is limited in its characteristic in comparison with a discrete photosensitive element. Namely, since higher performance is required for the semiconductor element, a photosensitive element has to be formed almost without changing the manufacturing process of the conventional semiconductor integrated circuit. Therefore, it is difficult for a photosensitive element to give and improve the predetermined characteristic. In such a case, improvement in characteristics of a photosensitive element can be realized by adding intrinsic manufacturing processes for formation of the photosensitive element. But, such addition of manufacturing process results in an increase in manufacturing costs.